This invention relates to molecular sieve catalysts that contain attrition particles. In particular, the invention is to molecular sieve catalysts that contain attrition particles recycled from a catalyst manufacture process or from a reaction system and virgin molecular sieve.
A molecular sieve is generally a microporous structure composed of either crystalline aluminosilicate, chemically similar to clays and feldspars and belonging to a class of materials known as zeolites, or crystalline aluminophosphates derived from mixtures containing an organic amine or quaternary ammonium salt, or crystalline silicoaluminophosphates which are made by hydrothermal crystallization from a reaction mixture comprising reactive sources of silica, alumina and phosphate. Molecular sieves have a variety of uses. They can be used to dry gases and liquids; for selective molecular separation based on size and polar properties; as ion-exchangers; as catalysts in cracking, hydrocracking, disproportionation, alkylation, isomerization, oxidation, and conversion of oxygenates to hydrocarbons, particularly alcohol and di-alkyl ether to olefins; as chemical carriers; in gas chromatography; and in the petroleum industry to remove normal paraffins from distillates.
Molecular sieves are manufactured by reacting a mixture of several chemical components. One of the components used in the reaction process is a template, although more than one template can be used. The templates are used to form channels or tunnel like structures (also called a microporous structure) within the composition. When the template is removed, an open microporous structure is left behind in which chemical compositions can enter, as long as the chemical compositions are small enough to be able to fit inside the tunnels. Thus a molecular sieve acts to sieve or screen out large molecules from entering a molecular pore structure.
Molecular sieves are particularly desirable for use as catalytic agents. The molecular sieves that act as catalysts have catalytic sites within their microporous structures. Once the template is removed, a chemical feedstock that is small enough to enter into the tunnels can come into contact with a catalytic site, react to form a product, and the product can leave the molecular sieve through any number of the tunnels or pores as long as the product has not become too large to pass through the structure. The pore sizes typically range from around 2 to 10 angstroms in many catalytic molecular sieves.
To be useful in commercial scale catalytic reaction systems, molecular sieves are generally composited with other catalytic or inert structure affecting components to form finished catalyst particles. Such particles are described, for example, in U.S. Pat. No. 4,499,327.
Although finished catalyst particles are generally harder than the molecular sieve components, they are prone to damage due to physical stresses encountered during the manufacture of the finished catalyst particles or during the use of the finished catalyst particles in a reaction system. This damage tends to physically wear down or break apart (i.e., attrit) the catalyst particle until it is too small to efficiently recapture for reuse. The attritted particle is then discarded as waste from the system in which it is used.
In the manufacture of finished catalyst particles, there may also be produced particles that are too large for subsequent use in a reaction system. For example, through misoperation of equipment or transient operations at the beginning or end of one cycle of a batch catalyst manufacturing operation, large clumps or sheets of the sieve or composite material may form on the walls or floors of equipment. The clumps are then discarded as a loss in the catalyst manufacturing process.
The discarding of catalyst attrition particles or oversized catalyst clumps is problematic from an economic standpoint. Therefore, methods for effectively recovering and reusing these attrition particles and clumps are highly desired.
In order to limit losses of molecular sieve-containing attrition particles and/or clumps during manufacture or during use, this invention provides a catalyst composition which comprises molecular sieve-containing attrition particles; virgin molecular sieve; and binder. The virgin molecular sieve can include dried attrition particles and/or catalyst clumps. The molecular sieve-containing attrition particles can include virgin molecular sieve and binder or calcined molecular sieve catalyst particles which contain molecular sieve and binder.
In another embodiment, the invention is to a method of making a molecular sieve catalyst composition which comprises mixing together molecular sieve-containing attrition particles, virgin molecular sieve components and binder. The mixture is then dried to form the molecular sieve catalyst composition.
In yet another embodiment, the invention is to a method of making olefins from an oxygenate feedstock. The method comprises providing a catalyst composition that contains attrition particles, virgin molecular sieve, and binder; and contacting the catalyst composition with oxygenate to form an olefin product.
The invention also includes a method of recycling molecular sieve-containing attrition particles to form a catalytic composition. The method comprises recovering the molecular sieve-containing attrition particles from a calciner process unit; mixing at least 40% the recovered molecular sieve-containing attrition particles with virgin molecular sieve components; and compositing the mixture to form a catalyst composition.
Desirably, the molecular sieve-containing attrition particles have a catalytic activity that is at least 25% of the catalytic activity of the corresponding virgin molecular-sieve containing particles. It is also desirable that the catalyst composition have an average particle diameter which ranges from 40 xcexcm to 150 xcexcm, and the molecular sieve-contains attrition particles which have an average particle diameter of less than 20% of the average particle diameter of the catalyst composition. In a desired embodiment, the molecular sieve-containing attrition particles comprise less than 20 wt. % coke.
In another desired embodiment of the invention, the molecular sieve of the molecular sieve-containing attrition particles is selected from the group consisting of SAPO-5, SAPO-8, SAPO-11, SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO-31, SAPO-34, SAPO-35, SAPO-36, SAPO-37, SAPO-40, SAPO-41, SAPO-42, SAPO-44, SAPO-47, SAPO-56, the metal containing forms thereof, and mixtures thereof. More preferably the molecular sieve of the molecular sieve containing attrition particles is selected from the group consisting of SAPO-17, SAPO-18, SAPO-34, SAPO-35, SAPO-44, and SAPO-47; most preferably SAPO-18 and SAPO-34, including the metal containing forms thereof, and mixtures thereof.
The molecular sieve in the molecular sieve-containing attrition particles and the virgin molecular sieve can have the same framework composition or they can have different framework compositions. In addition, the catalyst can further comprise erosion material selected from the group consisting of aluminum, iron, cobalt, vanadium, nickel, silicon, and combinations thereof.
The reaction process readily takes place when the catalyst composition is contacted with the oxygenate feed. Preferably, the catalyst composition is contacted with the oxygenate at a temperature of from 200xc2x0 C. to 700xc2x0 C.; a weight hourly space velocity of from 1 hrxe2x88x921 to 1000 hrxe2x88x921; and a pressure of from 0.5 kPa to 5 MPa. The olefin product preferably comprises ethylene, propylene or a combination thereof.